The present disclosure relates, in various exemplary embodiments, to display devices comprising light-absorbing layers. The light-absorbing layers comprise metal nanoparticles in a matrix material. While the light-absorbing layers are described with particular reference to organic light emitting devices (OLEDs), it will be appreciated that the light-absorbing layers comprising the metal nanoparticles are amenable to other similar applications and display devices.
Organic light emitting devices (OLEDs) represent a promising technology for display applications. A typical organic light emitting device includes a first electrode; a luminescent region comprising one or more electroluminescent organic material(s); and a second electrode; wherein one of the first electrode and the second electrode functions as a hole-injecting anode, and the other electrode functions as an electron-injecting cathode; and wherein one of the first electrode and the second electrode is a front electrode, and the other electrode is a back electrode. The front electrode is transparent (or at least partially transparent) while the back electrode is usually highly reflective to light. When a voltage is applied across the first and second electrodes, light is emitted from the luminescent region and through the transparent front electrode. When viewed under high ambient illumination, the reflective back electrode reflects a substantial amount of the ambient illumination to the observer, which results in higher ratios of reflected illumination as compared to the device's own emission resulting in “washout” of the displayed image.
In order to improve the contrast of electroluminescent displays in general, light-absorbing layers as described, for example, in U.S. Pat. No. 4,287,449, or optical interference members as described, for example, in U.S. Pat. No. 5,049,780, have been used to reduce the ambient illumination reflection.
Another problem of known organic light emitting devices originates from the use of metals with low work functions, and hence high reactivity, in the cathodes. Due to their high reactivity, such cathode materials are unstable in ambient conditions and react with atmospheric O2 and water to form non-emissive dark spots. See, for example, Burrows et al., “Reliability and Degradation of Organic Light Emitting Devices,” Appl. Phys. Lett. Vol. 65, pp. 2922-2924 (1994). To reduce such ambient effects, organic light emitting devices are typically hermetically sealed, immediately after fabrication, under stringent conditions, such as, for example, less than 10 ppm moisture atmospheres.
Other recent developments in reducing the reflection of ambient light in display devices have been directed to metal-organic mixed layers such as described in, for example, U.S. patent application Ser. No. 10/117,812, which is published as U.S. Patent Publication No. 2002/0180349, now U.S. Pat. No. 6,841,932, and U.S. patent application Ser. No. 10/401,238, which is published as U.S. Patent Publication No. 2003/0234609. Other methods to reduce light reflection are addressed in U.S. Pat. No. 6,750,609. These applications and patents are incorporated herein by reference in their entirety.
Other documents that may be relevant to the present application include the following: U.S. Pat. No. 4,652,794; U.S. Pat. No. 6,023,073; Liang-Sun Hung, et al., “Reduction of Ambient Light Reflection in Organic Light-Emitting Diodes,” Advanced Materials Vol. 13, pp. 1787-1790 (2001); Liang-Sun Hung, et al., U.S. patent application Ser. No. 09/577,092 (filed May 24, 2000); EP 1 160 890 A2 (claims priority based on above U.S. patent application Ser. No. 09/577,092; Japanese laid open patent document No. 8-222374 (laid open date Aug. 30, 1996); O. Renault, et al., “A low reflectivity multilayer cathode for organic light-emitting diodes,” Thin Solid Films, Vol. 379, pp. 195-198 (2000); WO 01/08240 A1; WO 01/06816 A1; David Johnson, et al., Technical Paper 33.3, “Contrast Enhancement of OLED Displays,” http://www.luxell.com/pdfs/OLED tech ppr.pdf, pp. 1-3 (April 2001); Junji Kido, et al., “Bright organic electroluminescent devices having a metal-doped electron-injecting layer,” Applied Physics Letters Vol. 73, pp. 2866-2868 (1998); Jae-Gyoung Lee, et al., “Mixing effect of chelate complex and metal in organic light-emitting diodes,” Applied Physics Letters Vol. 72, pp. 1757-1759(1998); Jingsong Huang, et al., “Low-voltage organic electroluminescent devices using pin structures,” Applied Physics Letters Vol. 80, pp. 139-141 (2002); L. S. Hung, et al., “Sputter deposition of cathodes in organic light emitting diodes,” Applied Physics Letters, Vol. 86, pp. 4607-4612 (1999); EP 0 977 287 A2; EP 0 977 288 A2; Hany Aziz, et al., “Reduced reflectance cathode for organic light-emitting devices using metal organic mixtures,” Applied Physics Letters Vol. 83, pp. 186-188 (2003); and, H. Michelle Grandin et al., “Light-Absorption Phenomena in Novel Low-Reflectance Cathodes for Organic Light-Emitting Devices Utilizing Metal-Organic Mixtures,” Advanced Materials, Vol. 15, No. 23, 2021-2024 (2003).
The entire disclosures of the foregoing patents, applications, and articles are each incorporated herein by reference in their entirety.
Other documents that may be relevant to the present application were submitted in U.S. patent application Ser. No. 09/800,716 (filed Mar. 8, 2001), now abandoned, such other documents being: U.S. Pat. No. 4,885,211; U.S. Pat. No. 5,247,190; U.S. Pat. No. 4,539,507; U.S. Pat. No. 5,151,629; U.S. Pat. No. 5,150,006; U.S. Pat. No. 5,141,671; U.S. Pat. No. 5,846,666; U.S. Pat. No. 5,516,577; U.S. Pat. No. 6,057,048; U.S. Pat. No. 5,227,252; U.S. Pat. No. 5,276,381; U.S. Pat. No. 5,593,788; U.S. Pat. No. 3,172,862; U.S. Pat. No. 4,356,429; U.S. Pat. No. 5,601,903; U.S. Pat. No. 5,935,720; U.S. Pat. No. 5,728,801; U.S. Pat. No. 5,942,340; U.S. Pat. No. 5,952,115; U.S. Pat. No. 4,720,432; U.S. Pat. No. 4,769,292; U.S. Pat. No. 6,130,001; Bemius, et al., “Developmental progress of electroluminescent polymeric materials and devices,” SPIE Conference on Organic Light Emitting Materials and Devices III, Denver, Colo., July 1999, SPIE, Vol. 3797, pp. 129-137; Baldo, et al., “Highly efficient organic phosphorescent emission from organic electroluminescent devices,” Nature Vol. 395, pp. 151-154 (1998); and, Kido, et al., “White light emitting organic electroluminescent device using lanthanide complexes,” Jpn. J. Appl. Phys. Vol. 35, pp. L394-L396 (1996).
All of the above patents, applications and articles are incorporated by reference in their entirety.
There is still a need to provide compositions suitable for use in a light-absorbing layer for display devices. Additionally, there is also a need to provide new configurations of light-absorbing layers suitable for use in a display device.